Communication devices such as wireless communication devices, that simply may be named wireless devices, may also be known as e.g. User Equipments (UEs), mobile terminals, wireless terminals and/or Mobile Stations (MS). A wireless device is enabled to communicate wirelessly in a wireless communication network, e.g. a cellular communications network, which may also be referred to as a wireless communication system, or radio communication system, sometimes also referred to as a cellular radio system, cellular network or cellular communication system. A wireless communication network may sometimes simply be referred to as a network and abbreviated NW. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more Core Networks (CN), comprised within the wireless communication network. The wireless device may further be referred to as a mobile telephone, cellular telephone, laptop, Personal Digital Assistant (PDA), tablet computer, just to mention some further examples. Wireless devices may be so called Machine to Machine (M2M) devices or Machine Type Communication (MTC) devices, i.e. a device that is not necessarily associated with a conventional user, such as a human, directly using the device. MTC devices may be as defined by the 3rd Generation Partnership Project (3GPP).
The wireless device may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.
The wireless communication network covers a geographical area which conventionally is divided into cell areas, wherein each cell area is served by at least one base station, or Base Station (BS), e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby e.g. also on cell size. A cell is typically identified by one or more cell identities. The base station at a base station site provides radio coverage associated with one or more cells and/or beams. Beams are further discussed below. A cell and beam may thus be associated with geographical areas, respectively, where radio coverage for the cell and beam, respectively, is provided by a base station at a base station site. Cells and/or beams may overlap so that several cells and/or beams cover the same geographical area. By a base station providing or serving a cell and/or beam is meant that the base station provides radio coverage such that one or more wireless devices located in the geographical area where the radio coverage is provided may be served by the base station in said cell and/or beam. When a wireless device is said to be served in or by a cell and/or beam this implies that the wireless device is served by the base station providing radio coverage for the cell and/or beam. One base station may serve one or several cells and/or beams. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the wireless device within range of the base stations.
The expression downlink, which may be abbreviated DL, is used for the transmission path from the wireless communication network, e.g. a base station thereof, to the wireless device. The expression uplink, which may be abbreviated UL, is used for the transmission path in the opposite direction i.e. from the wireless device to the wireless communication network, e.g. base station thereof.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunication System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communication (originally: Groupe Special Mobile).
In 3GPP Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or eNBs, may be directly connected to other base stations and may be directly connected to one or more core networks.
UMTS is a third generation mobile communication system, which may be referred to as 3rd generation or 3G, and which evolved from the GSM, and provides improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for wireless devices.
General Packet Radio Service (GPRS) is a packet oriented mobile data service on the 2G cellular communication system's global system for mobile communications (GSM).
Enhanced Data rates for GSM Evolution (EDGE) also known as Enhanced GPRS (EGPRS), or IMT Single Carrier (IMT-SC), or Enhanced Data rates for Global Evolution is a digital mobile phone technology that allows improved data transmission rates as a backward-compatible extension of GSM.
High Speed Packet Access (HSPA) is an amalgamation of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), defined by 3GPP, that extends and improves the performance of existing 3rd generation mobile telecommunication networks utilizing the WCDMA. Such networks may be named WCDMA/HSPA.
The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies, for example into evolved UTRAN (E-UTRAN) used in LTE.
Work is ongoing with developing a next generation wide area networks, which may be referred to as NeXt generation (NX), New Radio (NR), or fifth generation (5G). A design principle under consideration for 5G wireless communication networks is to base it on an ultra-lean design. This implies that “always on signals”, such as reference signals in LTE, shall be avoided in the network as much as possible. Expected benefits from this design principle include e.g. significantly lower network energy consumption, better scalability, higher degree of forward compatibility, lower interference from system overhead signals and consequently higher throughput in low load scenario, and also improved support for wireless device, or so called user, centric beam-forming.
Advanced Antenna Systems (AAS) is an area where technology has advanced significantly in recent years and where we also foresee a rapid technology development in the years to come. Advanced antenna systems in general and massive Multiple Input Multiple Output (MIMO) transmission and reception will likely be used in future wireless communication network and in 5G wireless communication networks.
A beam, such as mentioned above, is traditionally associated with transmission using so called beamforming, typically by means of a phase-adjustable, or phased, antenna array, the same underlying technique is equally applicable to reception. Beamforming, or spatial filtering, may be described as a signal processing technique for directional signal transmission and/or reception. This is typically achieved by combining elements in the phased antenna array, often referred to simply as a phased array, in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity. Thereby, thanks to directivity, improvements are possible to achieve compared with omnidirectional reception/transmission. For example, a transmitter may perform transmit beamforming by transmitting the same signal on all elements of a phased array, except for a per-element weight comprising a phase shift and an amplitude factor. Similarly, a receiver with an phased array, that may be the same and/or configured in the same way as of the transmitter, may perform receive beamforming by applying per-element weights and adding the resulting signals before further processing. The selectivity and directivity may thus be the same in transmission and reception. For transmission, it means that the signal will be stronger in some direction or directions and weaker in others. For reception, it means that signals from some direction or directions are amplified and those from other directions are attenuated, relative to each other. The same antenna may be used, i.e. operated, for transmission and reception although typically not at the same time.
Beams and beamforming may be applied in the uplink and/or downlink, and at both communication ends or only at one communication end. For example, in the downlink regarding communication between a wireless communication network and a communication device, the wireless communication network may uses transmit beamforming and/or the communication device may use receive beamforming. Correspondingly, in the uplink regarding communication between a wireless communication network and a communication device, the wireless communication network may use receive beamforming and/or the communication device may use transmit beamforming. Synonymous naming for transmit beamforming may be transmission beamforming or transmitting beamforming and synonymous naming for receive beamforming may be reception beamforming or receiving beamforming. Conventionally when referring to a beam, a transmit beam is meant, i.e. a radio beam formed and/or generated by transmit beamforming. However, as can be realized from above, it can as well make sense to refer to receive beams, i.e. beams associated with receive beamforming. Herein, “beam” typically refers to a transmit beam if nothing else is indicated, as should be recognized by the skilled person.
A beam provided by a network node is typically for communication with, e.g. for serving, one or a few (compared to a cell) communication devices at the same time, and may be specifically set up for communication with these. The beam may be changed dynamically by beamforming to provide desirable coverage for the one or few communication devices communicating using, e.g. being served by, the beam. A beam provided by a communication device is typically for communication with the wireless communication network, particularly one or a few radio network nodes thereof, typically one, or at least one, that is a main target for the beam.
A transmit beam may be associated with one or more identifiers and/or identities, which may by fix and/or dynamically assigned. There may be identifiers and/or identities that are the same for a set or group of beams, i.e. multiple beams, e.g. corresponding to a cell identity that is the same for all of said multiple beams, e.g. those within a cell, and/or there may be others that identify an individual beam, e.g. an individual beam within a cell or group of beams. A beam identifier and/or beam identity may directly identify the beam, and may e.g. be transmitted in the beam, and/or may indirectly identify the beam, e.g. by referring to the time and/or frequency of a received reference signal transmitted using that beam.
Beamforming improves performance both by increasing the received signal strength, thereby improving the coverage, and by reducing unwanted interference, thereby improving the capacity. Beamforming can be applied both in a transmitter and a receiver of a radio network node and/or wireless device. In a transmitter, beamforming may amount to configuring the transmitter to transmit the signal in a specific direction, or a few directions, and not in other directions. In a receiver, beamforming may amount to configuring the receiver to only receive signals from a certain direction, or a few directions, and not from other directions. When beamforming is applied in both the transmitter and the receiver for a given communication link, the beam pair may be referred to as the beams selected in the both ends. Generally, the beamforming gains are related to the widths of the used beams, where a relatively narrow beam provides more gain than a wider beam.
Beamforming requires some form of beam management, such as beam search, beam refinement, and/or beam tracking, to determine what transmit and receive beams, and e.g. directions thereof, to use for communication between two units, typically between a wireless device and a radio network node, such as a base station. Beam search may involve the transmitter sweeping a signal across several beams, to allow a receiver in an unknown direction to receive the signal. Beam search may also involve the receiver scanning across several receive beams, thereby being able to receive a signal from an initially unknown direction. Beam search typically also involves the receiver sending a message to a transmitter to indicate which transmit beam, or beams, are best suited for transmission to that receiver. Beam refinement and/or tracking is applied when a working beam or beam pair is already selected. Beam refinement is to improve the selected beams, for instance finding a narrower beam that provides a better gain. Beam tracking is to update the selected beam or beams when the conditions change, e.g. due to mobility. Beam refinement and tracking are typically performed by temporarily evaluating a different beam than the one that is currently used for communication, and switching to that beam if it is deemed better than the current.
Beam search may take considerable time, if there are many beams to search on both the transmitter and receiver side, and during this time communication is typically not possible. Beam refinement and tracking are usually ongoing activities that cause little or no disturbance to ongoing communication.
Networks will typically transmit periodic or continuous reference signals to support beam management, e.g. by sweeping across several transmit beams as describe above. Such transmissions are here referred to as Beam Reference Signals (BRS) or simply RS. Some aspects of beam management may then be performed by a wireless device with little or no explicit involvement from the network, since the wireless device may assume that the network is transmitting the BRS periodically or continuously. For instance, wireless device typically perform beam search as part of the system-acquisition procedure, resulting in a selection of a suitable network beam and wireless device beam. Then the terminal performs a random-access transmission using its selected wireless device beam using a transmission resource, associated with certain time and/or frequency, where it is expected that the network is able to receive random-access transmissions using the selected network beam. Wireless devices typically continue to receive BRS even when communication is ongoing, to search for new communication paths and to perform refinement and tracking of currently used beams.
Many wireless communication networks include some kind of radio-link supervision, where the quality of communication is regularly checked, and some action is taken in case the quality is unacceptable or the communication is lost. Radio-link supervision often involves a receiver, e.g. a wireless device or network node, checking the presence and/or quality of a sync signal or a reference signal. It may also involve monitoring a number of retransmissions in a retransmission protocol, and monitoring the time to receive a response to an earlier transmitted request message. In case any of these checks indicate a severe problem, the receiver, e.g. the wireless device or network node, often declares a radio-link failure and initiates some action. In case of a network node having lost communication with a wireless device, the action may involve releasing some or all network resources related to that wireless device. In case of a wireless device having lost communication with a network, the action may involve searching for synchronization and reference signals from the network and, in case such signals are found, attempting to access the network again. In case of a beamforming system, such actions typically involve beam search.